RAID (Redundant Array of Independent Disks) technology is becoming more prevalent for the purpose of increasing the reliability of storage apparatus. In recent years, storage apparatus equipped with RAID and thin provisioning have been adopted in order to reduce storage area and management costs.
With thin provisioning, a storage apparatus provides a virtual volume in the form of virtual storage area having a volume recognized by a host apparatus. Subsequently, when a write request has been issued from the host apparatus, the storage apparatus associates physical storage area with just the locations inside the virtual volume where data was allocated by the write request. The amount of physical storage area corresponds to the size of that data. In other words, the storage apparatus specifies a RAID group for each location inside the virtual volume, and allocates storage area to the disks inside the specified RAID group. The method for allocating physical storage area for each location might be controlled by the storage apparatus such that the sizes of already-allocated storage areas become evenly distributed among the RAID group.
However, if the disk storage areas allocated to locations inside the virtual volume by the storage apparatus are storage areas inside a RAID group that includes one or more damaged disks, there is a problem of reduced access performance for the storage apparatus as a whole. In other words, when allocating physical storage area to the virtual volume, the storage apparatus specifies a RAID group so as to evenly distribute the allocation size, without checking the state of each RAID group. For this reason, if the storage area allocated to the virtual volume is storage area from a RAID group that hypothetically includes one or more damaged disks, then when that RAID group is subsequently accessed, extra load will be incurred on the access processes, and response will be slower. As a result, the average response of the storage apparatus as a whole will be degraded.